1. Field of the Invention
The present invention relates to a sheet feeder and a printer suitable for an ink jet printing.
2. Description of the Related Art
A sheet sending roller of a known conventional printer sends sheets of paper one after one from the sheet hopper, where the sheets are stored. A sent sheet is fed between a cylindrical feed roller and a set of pressure rollers to the position in front of the print mechanism, where the sheet is printed. The presence of a sheet being fed can be detected by a detecting means fitted near the cylindrical feed roller. The detecting means may include a lever which can be pushed by a sheet, and a sensor for sensing the motion of the lever. By positioning the detecting means as near as possible to the nips each between the cylindrical roller and one of the pressure rollers, it is possible to detect a sheet accurately with the sheet less floating. It is also possible to control the front or rear end position (leading or trailing edges) of a sheet with the cylindrical roller and the pressure rollers with few errors relative to the print mechanism. In the case of a printer where the front end of a sheet is registered at the nips each between the cylindrical roller and one of the pressure rollers, it is further possible to confirm the presence of the sheet securely or certainly.
In the case of a printer where sheets of different widths can be set or stacked in contact with the side wall of the sheet hopper on the reference side, it is necessary to detect a sheet of any width by fitting a detecting means in the sheet passage on this side. In order to position the detecting means near the nips each between the cylindrical feed roller and one of the pressure rollers, it is necessary to form space for the means by cutting the rollers on the reference side. If the rollers are cut, an edge part of a sheet on the reference side of the sheet passage cannot be put between them. This part of a sheet may, due to the resistance of the next sheet and/or the sheet passage, be fed more slowly than other part fed between the cylindrical feed roller and the set of pressure rollers. As a result, a sheet may be fed in an inclined position relative to the feeding direction. In particular, if the detecting means includes a mechanical lever, the resistance of which acts in addition, more sheets may be fed in inclined positions. Consequently, even if the front end of a sheet is positioned and/or an inclination of this end is rectified by registration at the nips each between the cylindrical feed roller and the one of the pressure rollers, these rollers may feed the sheet in an inclined position because of lack of driving force for an edge part of the sheet on the reference side.
In order to prevent the inclination of the sheet feeding, the cylindrical feed roller of a certain printer has a peripheral or circumferential groove formed at a slight distance from the roller end on the reference side. The groove is faced by a detecting means. Because the rubber of the roller end part of the slight width is not stable, however, the desired feed cannot be achieved at this part, and the part may be broken.